Jonas Kubilius was a Lithuanian mathematician known for his work in probability theory and number theory. An educator by profession, he worked as a lecturer and professor at various prestigious institutions including the Vilnius University and the Lithuanian Academy of Sciences. He was also the rector of the Vilnius University for 32 years. Born into a farming family in a village in Lithuania, he began displaying his brilliance at a young age. Even as a school boy he loved to study and was especially interested in science and mathematics. He understood mathematical concepts with outstanding clarity and even helped his teacher in explaining difficult mathematic equations to fellow students while in school. He seemed to be on the right track to make a brilliant career for himself when the political situation in Europe became increasingly tense. In spite of the turbulent political atmosphere he bravely continued his studies, graduated from high school, and enrolled at the Vilnius University to further his education. Eventually he embarked on a teaching career and continued his own education by working for a Doctor of Science degree from the Steklov Institute of Mathematics in Moscow. Later on he joined the Lithuanian Academy of Sciences where he promoted his scientific work in the areas of number theory and probability theory

After receiving his Candidate’s degree, Jonas Kubilius started working at the Institute of Physics and Technology of the Lithuanian Academy of Sciences. He also took up a second part-time teaching position as a lecturer at the university in 1952, simultaneously working at two jobs.
In 1952, he published ‘On some problems of the geometry of prime numbers’ in which he developed the "analytical number-theory in n dimensions" introduced by Hecke and extended the theory with the use of more powerful methods.
By now he had set his eyes on writing a doctoral thesis. He was advised by Linnik to submit his thesis to the USSR Academy of Sciences rather than the Lithuanian Academy.
Unable to get into the USSR Academy of Sciences, Jonas Kubilius started working on his doctorate at the Steklov Institute of Mathematics in Moscow and received his Doctor of Science degree (habilitation) in 1957.
During the 1950s the Vilnius University was going through difficult times. Juozas Bulovas who became the Rector of the University in 1956 was trying to make the university “Lithuanian” by encouraging the use of the Lithuanian language in place of Russian and to revive the Department of Lithuanian Literature.
Bulovas also dismissed some of the poorly performing Soviet staff and re-employed some professors who were returning from their exile in Serbia. But these reforms did not go well with the Soviet authorities and Bulovas was dismissed as the rector.
Jonas Kubilius was offered the position vacated by Bulovas. Initially he was reluctant to accept it as he was afraid that taking up the role of the rector would interfere with his mathematical research. However, he decided to accept the position as he left that it was his moral duty to take forward the work that Bulovas had so passionately started during his tenure. Thus he became the rector of the university in 1958.
As the rector, he was successful in resisting the pressure to “Russify” the university and promoted the Lithuanian language and culture in the university. He also wrote several textbooks in Lithuanian and encouraged the faculty to write research papers in Lithuanian, English, German, and French along with Russian.
He also continued working on his mathematical research. His scientific work was primarily in the areas of number theory and probability theory.
In 1991, he retired from the position of the rector after serving for almost 33 years though he retained his position as a professor in the university.

Jonas Kubilius was born on 27 July 1921 in Fermos village, Eržvilkas county, Jurbarkas district municipality, Lithuania. He was from a family of farmers. He had four younger brothers.
He received his early education from Rudkiškiai grade school and Eržvilkas middle school before enrolling at the Raseiniai high school from where he graduated in 1940.
He was a good student and excelled in academics. His favorite subjects were mathematics and literature. He was particularly brilliant in mathematics and even helped his teacher in explaining difficult concepts to his class mates.
He entered the University of Vilnius to study mathematics and graduated summa cum laude in 1946. In between, he had taken a year off to teach mathematics in middle school.
After graduation, Jonas Kubilius was employed as an assistant in the Department of Physics and Mathematics. He held this position for two years (1946–48).
He then went to the Leningrad University to further his education and received the Candidate of Sciences degree in 1951 for his thesis ‘Geometry of Prime Numbers’.

Jonas Kubilius was happily married. He deeply loved his wife and the couple shared a happy marriage. They had a son Kestutis who became a mathematician and a daughter Birute who became a professor of medicine.
He lived a long and productive life and breathed his last on 30 October 2011, at the age of 90.